Turbocharger comprising a torsional-vibration damper

ABSTRACT

The invention relates to an exhaust-gas turbocharger, which is operated by the exhaust gas of a combustion engine and is equipped with a rotor unit that rotates at high-speed. Said rotor unit comprises a turbocharger shaft, a turbine wheel that is rotationally fixed to the shaft, in addition to a compressor wheel that is rotationally fixed to the shaft. To increase the operational reliability of said turbocharger, a torsional-vibration damper is located on the turbocharger shaft. The torsional-vibration damper reduces torsional-vibration stresses that arise in the shaft, which are caused by motor pulsations of a higher order of the combustion engine.

TECHNICAL FIELD

[0001] The invention relates to a turbocharger according to the features of the preamble of patent claim 1.

PRIOR ART

[0002] Turbo chargers are used for increasing the power of reciprocating piston engines. They possess a rapidly rotating rotor unit which comprises a turbine, a compressor and a shaft connecting the turbine and compressor. In exhaust gas turbochargers, the turbine of the turbocharger is operated by means of the exhaust gas from an internal combustion engine. The turbine drives the compressor by means of the common shaft. The gas compressed by the compressor is supplied to the combustion chambers of the engine for charging the latter. The pressure, acting upon the turbine, of the exhaust gas from the internal combustion engine is not constant, and this may excite the turbocharger shaft into vibrations. The pressure pulsations depend, inter alia, on the opening and closing characteristic of the outlet valves of the engine and on the configuration of the exhaust line. The predominating ignition frequency of the engine is clearly to the forefront in the frequency spectrum of these pressure pulsations, said ignition frequency depending on the number of cylinders, on the working process (2-stroke/4-stroke) and on the engine rotational speed. It is the state of the art to dimension the shaft of the turbocharger in such a way that all the characteristic torsional frequencies of the turbocharger shaft are well above the maximum possible ignition frequency of the engine. It has thereby been possible hitherto to avoid resonance between the main excitation and the characteristic torsional frequencies and to design the turbochargers so as to be operationally reliable.

[0003] More recent investigations and measurements have shown that higher engine orders also occur in the pressure pulsation spectrum in addition to the ignition frequency. These pressure pulsations of higher order may coincide with the characteristic torsional frequency of the turbocharger shaft. These resonant vibrations, which cannot be avoided in the case of variable engine rotational speed, lead to torsional stresses in the turbocharger shaft. In the past, however, the level of excitation was so low that, owing to the internal damping of the turbocharger shaft, the resonant vibrations led only to insignificant torsional stresses which were tolerable over the long term.

[0004] However, due to steeper camshaft flanks and also rising pressure conditions in engines and turbochargers, higher excitations and consequently higher torsional stresses in the turbocharger shaft are to be expected. The required increasing power density of the turbocharger shaft is a further factor which aggravates the problem. Inadmissibly high loads on the turbocharger shaft are therefore to be expected in future.

[0005] The only measure known hitherto for counteracting the loads caused by torsional vibrations in the turbomachines themselves is the selection of larger shaft diameters. However, this is associated with higher power losses in the shaft bearings of the turbocharger.

PRESENTATION OF THE INVENTION

[0006] The object of the invention is, therefore, to provide a cost-effective turbocharger with a rapidly rotating rotor unit, the operating reliability of which is ensured without efficiency losses, even in the event of the rising levels of excitation to be expected in future for torsional vibrations of the turbocharger shaft.

[0007] This object is achieved by means of a turbocharger according to the features of patent claim 1. The arrangement of a torsional vibration damper on the turbocharger shaft reduces the load on the turbocharger shaft caused by any occurring torsional vibrations and thus prevents critical load peaks. Operating reliability is thus ensured even in the case of configurations with steep camshaft flanks and/or rising pressure conditions in the engine and turbocharger.

[0008] The known principles of torsional vibration dampers, such as oil displacement dampers, rubber dampers, viscose torsional vibration dampers and silicone-oil rubber dampers, come into consideration. Such dampers known per se are described, for example, in “Berechnung des dynamischen Verhaltens von Viskosedrehschwingungs-dämpfern”, [“Calculation of the dynamic behavior of viscose torsional vibration dampers”], Dissertation TU Berlin, 1982, Dipl. Ing. Rainer Hartmann, pp. 9-13.

[0009] The dampers are advantageously arranged at the compressor-side shaft end, in particular on the inlet side of the compressor wheel hub, since the vibration deflections and consequently the damping action are at their greatest there. A further advantage is also the good cooling action in the case of a relatively constant and low temperature, this being advantageous for all forms of damper construction.

[0010] In an arrangement at the inlet of the compressor wheel, the outside diameter of the torsional vibration damper is selected such that it corresponds to approximately 80%-110%, most preferably to 90% to 100%, of the hub diameter of the compressor at the inlet. As a result, the radial construction space is utilized efficiently and the inflow of the compressor is not disturbed.

[0011] It may also be envisaged to arrange the damper in the region of the turbine, in which case it is necessary to ensure that materials with sufficient heat resistance are used.

[0012] It is likewise advantageous to arrange the torsional vibration damper between the turbine wheel and the compressor wheel. Since the construction space which is present there is larger, above all, in the radial direction, the dimensioning of the damper is simpler.

[0013] The use of a viscose torsional vibration damper has proved particularly advantageous. An annular rotary mass is mounted freely rotatably on the inside in a housing. A viscous medium is introduced in the gap between ring and housing and, in the event of relative movements between the two parts, generates a damping action as a result of the shearing forces which arise. In this case, it is particularly important to stabilize the damper temperature. The damper is therefore advantageously arranged at the inlet of the compressor wheel. The air stream with very high flow velocities in the inlet region of the compressor ensures an optimum cooling of the damper and consequently a largely uniform temperature of the damper.

[0014] Depending on the design of the turbocharger and on the torsional vibration loads which occur, it may be advantageous to arrange a plurality of torsional vibration dampers on the turbocharger shaft instead of one torsional vibration damper. In this case, identical or different torsional vibration dampers may be used in accordance with the load, and they may be provided directly next to one another or at various locations on the shaft.

[0015] Further preferred embodiments are the subject matter of further dependent patent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The subject of the invention is explained in more detail below with reference to preferred exemplary embodiments illustrated in the accompanying purely diagrammatic drawings, in which:

[0017]FIG. 1 shows, in a section along its longitudinal axis, a turbocharger with a torsional vibration damper in the region of, the compressor inlet;

[0018]FIG. 2 shows the turbocharger from FIG. 1 with a torsional vibration damper in the region between the compressor wheel and turbine wheel;

[0019]FIG. 3 shows the result of a measurement of the amplitude of the torsional vibration on a turbocharger shaft with torsional vibration damper; and

[0020]FIG. 4 shows the result of a measurement of the amplitude of the torsional vibration on a turbocharger shaft with torsional vibration damper.

[0021] The reference symbols used in the drawings and their significance are collated in the list of reference symbols. Basically, identical parts are given the same reference symbols in the figures. The embodiment described stands as an example of the subject of the invention and has no restrictive effect.

WAYS OF CARRYING OUT THE INVENTION

[0022]FIGS. 1 and 2 each show a turbocharger 10 with a rapidly rotating rotor unit 11 in a section along their longitudinal axes 18. Each rapidly rotating rotor unit 11 comprises a turbine 12 and a compressor 16 which are connected to one another via a common, turbocharger shaft 14. The turbine 12 has a turbine wheel 22, surrounded by a turbine housing 20 and having turbine blades 23. The compressor wheel 26 has compressor blades 27 which are distributed regularly over the circumference of a compressor wheel hub 25. The compressor wheel 26 is surrounded by a compressor housing 24 and can be driven by the turbine 12 by means of the common shaft 14. The common turbocharger shaft 14 is mounted between the compressor wheel 26 and the turbine wheel 22 in a bearing housing 28.

[0023] The turbine housing 20 forms a flow duct 29 which is connected (not illustrated) to the exhaust line of an internal combustion engine. The flow duct 29 leads via the turbine wheel 22 and makes it possible, via a gas outlet housing 30 of the turbine housing 20, to discharge the exhaust gas of the internal combustion engine from the turbocharger 10. The compressor housing forms a second flow duct 32, via the inlet 34 of which air or another combustible gas is sucked in, led via the compressor wheel 26 and at the same time compressed. The compressed gas is finally discharged from the turbocharger 10 via an outlet, not explicitly illustrated, of the compressor housing 24 and into a feed line of the internal combustion engine (not illustrated).

[0024] The pressure pulses which are transmitted to the turbocharger shaft 14 by the exhaust gas of the internal combustion engine according to its engine order when said exhaust gas flows over the turbine wheel 26 are damped by means of a torsional vibration damper 36. In the example shown here, this is a viscose torsional vibration damper which is secured fixedly in terms of rotation to the shaft 14 on the inlet side upstream of a compressor hub 25 of the compressor wheel 26. By virtue of this positioning, it is possible for the viscose torsional vibration damper to be cooled optimally by the gas flowing in. Moreover, the torsional vibration damper is thus located in the region of the highest torsional vibration amplitudes of the shaft 14 and can therefore exert its greatest action. In this example, the radial extent of the torsional vibration damper 36 amounts to 100% of the radial extent of the compressor wheel hub 25 in the region of the latter which follows the torsional vibration damper 36. The construction space is thereby utilized optimally, without the flow via the compressor wheel 26 being impeded.

[0025] The turbocharger 10 in FIG. 2 is identical to the turbocharger 10 from FIG. 1. The torsional vibration damper 36 for reducing the torsional vibration load on the shaft 14, however, is not connected fixedly in terms of rotation to the turbocharger shaft 14 in the region of the compressor wheel 26, but, instead, between the compressor wheel 26 and turbine wheel 22 in the region of the bearing housing 28 of the turbocharger 10. The greater radial construction space can advantageously be utilized here, thus giving the torsional vibration damper 36 a higher efficiency. This higher efficiency, admittedly, cannot always have a full effect on dampening efficiency because of the greater proximity to the nodal point of the torsional vibration. Owing to the poorer cooling possibilities, a rubber damper is used here instead of a viscose torsional vibration damper.

[0026]FIGS. 3 and 4 show, by way of example, results of two measurements of the torsional vibration amplitudes on a turbocharger shaft, on the one hand, without a torsional vibration damper in FIG. 3, and, on the other hand, with a torsional vibration damper in FIG. 4. The measurements are based on the use of a viscose torsional vibration damper in the region of the inlet of the compressor. The vibration frequency of the torsional vibration is plotted at the top in Hertz and the rotational speed is plotted on the right in revolutions per second. The engine orders 40 which occur are plotted diagonally. The increased amplitudes 42 of the torsional vibrations 44 in the region of the associated exciting engine order 40 can be seen clearly in both figures. However, the level of the amplitudes 42 in FIG. 4, measured on the turbocharger shaft with a torsional vibration damper, is substantially lower than in FIG. 3, measured on the turbocharger shaft without a torsional vibration damper. These results show that the use of torsional vibration dampers in turbochargers can contribute considerably to the operating reliability of the turbochargers.

List of Reference Symbols

[0027]10 Turbocharger

[0028]12 Turbine

[0029]14 Shaft

[0030]16 Compressor

[0031]18 Longitudinal axis

[0032]20 Turbine housing

[0033]22 Turbine wheel

[0034]23 Turbine blades

[0035]24 Compressor housing

[0036]25 Compressor-wheel hub

[0037]26 Compressor wheel

[0038]27 Compressor blades

[0039]28 Flow duct

[0040]30 Gas outlet housing

[0041]32 Flow duct

[0042]34 Inlet

[0043]36 Torsional vibration damper

[0044]40 Engine order

[0045]42 Torsional vibration amplitude

[0046]44 Torsional vibration 

1. An exhaust gas turbocharger with a rapidly rotating rotor unit which comprises a turbocharger shaft, a turbine wheel connected fixedly in terms of rotation to the shaft, and a compressor wheel connected fixedly in terms of rotation to the shaft, the exhaust gas turbocharger being capable of being connected to an internal combustion engine and the rotor unit being capable of being operated by means of the exhaust gases from the internal combustion engine, wherein the exhaust gas turbocharger comprises means for the damping of torsional vibrations of the turbocharger shaft which are excited by higher engine orders of the internal combustion engine when the exhaust gas turbocharger is in the state connected to the internal combustion engine, the damping means comprising, a torsional vibration damper arranged on the shaft.
 2. The turbocharger as claimed in claim 1, wherein the torsional vibration damper is a viscose torsional vibration damper.
 3. The turbocharger as claimed in claim 1, wherein the torsional vibration damper is an oil displacement damper.
 4. The turbocharger as claimed in claim 1, wherein the torsional vibration damper is a rubber damper.
 5. The turbocharger as claimed in claim 1, wherein the torsional vibration damper is a silicone-oil rubber damper.
 6. The turbocharger as claimed in claim 1, wherein the torsional vibration damper is secured to the turbocharger shaft in the region of the compressor, and, in particular, on the inlet side upstream of a compressor hub of the compressor wheel.
 7. The turbocharger as claimed in claim 6, wherein the outside diameter of the torsional vibration damper is about 80% to 110%, preferably 90% to 100%, of the outside diameter of the compressor hub in that region of the compressor hub which follows the device.
 8. The turbocharger as claimed in claim 1, wherein the torsional vibration damper is arranged between the compressor wheel and the turbine wheel or in the region of the turbine.
 9. The turbocharger as claimed in claim 1, wherein more than one torsional vibration damper is arranged on the turbocharger shaft, in which case the torsional vibration dampers may be arranged at various locations on the shaft and various types of torsional vibration dampers may be provided. 